Thin film forming method

ABSTRACT

A substrate processing method for filling a gap without seams or voids comprising: providing a substrate with a gap in a reaction chamber, pumping down the reaction chamber to a pressure at or below 5 Torr and filling the gap with a film by alternately and sequentially supplying a precursor, a reactant and a radio frequency electromagnetic radiation comprising a relatively high radio frequency component and a relatively low radio frequency component.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims the benefit of and priority to U.S. Provisional Application No. 63/004,425, filed on Apr. 2, 2020 in the United States Patent and Trademark Office, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND 1. Technical Field

This disclosure provides a method for filling a gap, more particularly, a method for filling a gap without seams or voids.

2. Description of Related Art

In a gap-fill process for a semiconductor manufacturing process, an atomic layer deposition or plasma enhanced atomic layer deposition method may be used to deposit a seamless and/or void-free uniform film on the deep bottom portion of the pattern. A crack may occur in the film filling the trench when it goes through a subsequent heat treatment.

FIG. 1 shows a crack occurring in the film filling a gap and spreading to the top surface of the trench in the subsequent heat treatment. In FIG. 1, in the subsequent heat treatment step after filling a gap, shrinkage stress works on the film towards the side surface of the trench and causes a void 1 or a crack 2. Therefore, the film may need to be dense and hard to minimize the film shrinkage, especially a film on the side surface of the trench. Usually film shrinkage may be inversely proportional to a wet etch resistance. That is, a film with high wet etch resistance may be dense and shrink less, but a film with low wet etch resistance may be less dense and shrink more. So, by controlling a wet etch resistance, a film shrinkage may be controlled.

Radicals in plasma process may be used to make a film denser and improve wet etch resistance since radicals enhance an ion-bombardment effect to a film. For example, when a film is deposited on the inner surface of the trench in gap-fill process, a radio frequency electromagnetic radiation is supplied. For example, higher radio frequency electromagnetic radiation such as RF power and/or longer radio frequency electromagnetic radiation supply time may be applied to make a film denser and improve a wet etch resistance of the film.

FIG. 2 shows a wet etch rate (WER) of SiO₂ film per position of the trench in which a crack occurs in the film. As illustrated in FIG. 2, a wet etch resistance of SiO₂ in the top portion of the trench may be higher and denser than the wet etch rate of SiO₂ film in the middle (side) and the bottom portion, and the non-uniform wet etch resistance along the vertical direction of the film in the gap may cause a difference of shrinkage and a crack in the film. Therefore, the difference of wet etch resistance in the film may need to be reduced and more radicals may need to be moved to the bottom portion of the trench to make a film denser and prevent a crack from occurring there. To this end, a magnitude of radio frequency electromagnetic radiation, e.g. RF power may be increased and/or a radio frequency electromagnetic radiation supply time may be increased.

Increasing RF power may generate a parasitic plasma in/around the reaction space and trigger unsafe situations such as RF power discharge to the outside of the substrate processing apparatus, and increasing an RF power supply time may lower the productivity. Also, it may be more difficult for radicals to reach the bottom portion of the trench as the aspect ratio of the trench may get higher. Therefore, this invention provides a method that makes a film denser and improves a wet etch resistance of a film in the bottom portion of the trench with high aspect ratio, prevents a crack from occurring in the film and does not trigger the safety issue and lower the productivity.

SUMMARY

This disclosure provides a method for filling a gap and forming a film with high wet etch resistance.

In an embodiment according to the disclosure a gap is filled by providing a substrate with a trench in a reaction chamber, pumping down the reaction chamber to a pressure at or below 5 Torr, supplying a precursor and a reactant alternately and sequentially, wherein the reactant is activated by supplying a radio frequency electromagnetic radiation comprising a relatively high radio frequency component, and a relatively low radio frequency component.

In another embodiment according to this disclosure, a gap is filled by providing a substrate with a trench in a reaction chamber, pumping down the reaction chamber to a pressure at or below 5 Torr, supplying a precursor and a reactant alternately and sequentially, wherein the reactant is activated by a radio frequency electromagnetic radiation comprising a relatively high radio frequency component and a relatively low radio frequency component, wherein the relatively high radio frequency and the relatively low radio frequency are partially overlapped.

In another embodiment according to this disclosure, a gap is filled by providing a substrate with a trench in a reaction chamber, pumping down the reaction chamber to a pressure at or below 5 Torr, supplying a precursor and a reactant alternately and sequentially, wherein the reactant is activated by a radio frequency electromagnetic radiation comprising a relatively high radio frequency component and a relatively low radio frequency component, wherein the relatively high radio frequency component and the relatively low radio frequency component RF power are supplied in pulses of duty ratio of approximately 10% to 75%.

In another embodiment according to this disclosure, a gap is filled by providing a substrate with a trench in a reaction chamber, pumping down the reaction chamber to a pressure at or below 5 Torr, supplying a precursor and a reactant alternately and sequentially, wherein the reactant is activated by a radio frequency electromagnetic radiation comprising a relatively high radio frequency component and a relatively low radio frequency component, wherein the power ratio of the high radio frequency component and the low radio frequency component is approximately 1 to 1 to 3 to 1 adjusted to form a uniform film in density throughout the gap.

BRIEF DESCRIPTION OF THE DRAWINGS

The above and other aspects, features, and advantages of certain embodiments of the disclosure will be more apparent from the following description taken in conjunction with the accompanying drawings, in which:

FIG. 1 is a view of gap fill and its problem according to the existing substrate processing method.

FIG. 2 is a view of difference of WER of SiO₂ film per position in a gap when a crack occurs.

FIGS. 3A and 3B are view of concept of the existing substrate processing method and the substrate processing method according to one embodiment.

FIG. 4A and FIG. 4B are views of more detailed process sequence of the existing substrate processing method and the substrate processing method according to one embodiment.

FIG. 5 is a graph showing WER of SiO₂ film by pressure depending on the position in the gap.

FIG. 6 is a graph showing WER of SiO₂ film by low radio frequency component depending on the position in the gap.

FIG. 7 is a graph showing WER of SiO₂ film by process pressure and radio frequency components at the side-bottom portion of the gap.

FIG. 8A and FIG. 8B are views of another embodiment according to the disclosure.

FIG. 9 is a view of a duty ratio.

FIG. 10 is a view of substrate processing apparatus for processing a substrate according to the disclosure.

DETAILED DESCRIPTION

In one embodiment according to this disclosure, a dual radio frequency electromagnetic radiation and a low process pressure may be applied to form a film in a gap.

FIG. 3 schematically shows an embodiment of a substrate processing method according to this disclosure. The film may be deposited by a PEALD method. FIG. 3A may be the PEALD process using a single frequency RF power and FIG. 3B may be a PEALD process using dual radio frequency electromagnetic radiation. In FIG. 3B a relatively high radio frequency component with 13.56 MHz frequency and a relatively low radio frequency component with 430 kHz frequency may be provided to the process. The substrate processing method according to FIG. 3B may be carried out at lower process pressure than that of the process in FIG. 3A. That is, in the process a relatively high radio frequency component may be applied to have a uniform wet etch resistance regardless of the depth of the trench. This may increase the density of radicals and the ion bombardment effect so that the density of the film may be increased. A relatively low radio frequency component may be applied as well to increase the mean free path of radicals. The process according to this disclosure may be carried out at low process pressure to reduce the probability of collision between radicals and other gas molecules so that more radicals may reach the bottom portion of the gap. Therefore, by combining the above three factors, i.e. relatively high radio frequency component, relatively low radio frequency component and low process pressure, more radicals may reach the bottom of the gap and form denser film uniformly in the bottom portion of the gap.

FIG. 4 shows the process sequences of FIG. 3 in more detail. FIG. 4 illustrates a process sequence to deposit SiO₂ film by PEALD on the substrate. FIG. 4A is the existing substrate processing method in which Si-containing precursor is provided intermittently and oxygen reactant and Ar purge gas are continuously provided. A 13.56 MHz high radio frequency component of a radio frequency electromagnetic radiation is solely supplied intermittently in-situ and oxygen gas is activated to react with silicon molecules adsorbed on the substrate to form SiO₂ film at radio frequency component supplying step. FIG. 4B is a substrate processing method according to this disclosure in which not only 13.56 MHz high radio frequency component but also 430 kHz low radio frequency component of the radio frequency electromagnetic radiation are supplied at the same time. In FIG. 4B a process pressure is lower than the process pressure in FIG. 4A. The high radio frequency component and the low radio frequency component may be supplied in-situ as shown in FIG. 4, but the high radio frequency component and the low radio frequency component may be supplied remotely or at least one of high radio frequency component and the low radio frequency component may be supplied in-situ.

As described above, a high radio frequency component increases a radical density and ion bombardment effect, and contributes to forming a dense film accordingly. A low radio frequency component increases mean free paths of ions so that a wide range of film may become dense uniformly. A low process pressure reduces a probability of collusion between radicals and other gas molecules so that more radical ions can reach the bottom of the gap. By combining these three factors, more radicals reach the bottom of the gap and a dense film may be uniformly formed throughout the gap. In FIG. 4B the substrate processing sequence is repeated N times until the gap is filled with SiO₂ film.

Table 1 below shows a detailed experimental condition of another embodiment according to this disclosure.

TABLE 1 Process condition Temperature (° C.) 300 to 600° C., preferably 450 to 550° C. Process pressure (Torr) 1 to10 Torr, preferably 3 to 5 Torr Si source silicon-containing precursor, preferably aminosilane precursor Gas flow Purge Ar 6,000 to 10,000 sccm, preferably 7,000 rate(sccm) to 9,000 sccm Source carrier 1,000 to 3,000 sccm, preferably 1,500 to Ar 2,500 sccm Reactant(O2) 1,000 to 3,000 sccm, preferably 1,500 to 2,500 sccm Plasma High frequency 13.56 MHz, 600 to 1,500 W, preferably condition RF power 900 to 1,200 W Low frequency 430 kHz, 50 to 500 W, preferably 100 to RF power 300 W Plasma ignition 0.1 to 1.5 sec, preferably 0.3 to 1 sec time(sec) Process Source feeding 0.1 to 10 sec, preferably 0.2 to 5 sec time per Purge 0.1 to 10 sec, preferably 0.2 to 5 sec cycle (sec) RF plasma 0.1 to 10 sec, preferably 0.2 to 5 sec Purge 0.1 to 10 sec, preferably 0.2 to 5 sec Wet etch condition 100: 1 DHF, 1 minute

As described in Table 1, a SiO₂ film may be formed at 550° C., between 3 Torr and 5 Torr of process pressure. A SiO₂ film may be formed by supplying a silicon-containing precursor and an oxygen reactant. A silicon-containing precursor may be an aminosilane precursor. But the silicon precursor may not be limited thereto and silicon halide and iodosilane may be used as silicon-containing precursor. For instance, DIPAS, SiH₃N(iPr)₂, TSA, (SiH₃)₃N, DSO, (SiH₃)₂, DSMA, (SiH₃)₂NMe, DSEA, (SiH₃)₂Net, DSIPA, (SiH₃)₂N(iPr), DSTBA, (SiH₃)₂N(tBu), DEAS, SiH₃NEt₂, DTBAS, SiH₃N(tBu)₂, BDEAS, SiH₂(NEt₂)₂, BDMAS, SiH₂(NMe₂)₂, BTBAS, SiH₂(NHtBu)₂, BITS, SiH₂(NHSiMe₃)₂, TEOS, Si(OEt)₄, SiCl₄, HCD, Si₂Cl₆, 3DMAS, SiH(N(Me)₂)₃, BEMAS, SiH₂[N(Et)(Me)]₂, AHEAD, Si₂(NHEt)₆, TEAS, Si(NHEt)₄, Si₃H₈, DCS, SiH₂Cl₂, SiHI₃, SiH₂I₂ may be used as silicon-containing precursor and at least one of those precursors may be provided to the substrate. Besides oxygen gas, at least one of O₃, N₂O and CO₂ as reactant may be provided. The oxygen reactant may work as a reactive purge gas so that oxygen may be continuously provided to the substrate and activated by a radio frequency electromagnetic radiation and react with silicon molecules adsorbed on the substrate to turn into silicon oxide layer, but not react with silicon molecules when a radio frequency electromagnetic radiation is not provided and just purge the reaction by-products and the reaction space. In the process, 900 to 1200 W of high radio frequency component and 0.1 to 300 W of low radio frequency component are supplied to the reaction space simultaneously. The hardness or density of SiO₂ film deposited in the gap is measured by measuring a wet etch rate of the film. In this invention a WER (Wet Etch Rate) is measured by dipping the specimen into a diluted HF solution (100:1) for one minute.

FIG. 5 shows a wet etch rate of SiO₂ film per position of the gap after filling a gap with SiO₂ film, followed by wet-etching according to the condition in Table 1. In FIG. 5 a substrate processing process is carried out at 3 Torr and 5 Torr of process pressure respectively with common condition of 900 W of high radio frequency component supplied for one second. As shown in FIG. 5, the WER of SiO₂ film becomes higher as the gap becomes deeper. This indicates that the wet etch resistance is lower in the bottom portion of the trench than the wet etch rate of the top portion and the mobility of radicals is inversely proportional to the depth of the gap. FIG. 5 also shows that the wet etch resistance at the side-bottom portion changes greatly depending on the process pressure. That is, the wet etch resistance of a film at the side-bottom portion of the gap improves more at low process pressure since the collision between radicals and other gas molecules are reduced at low process pressure and more radicals reach the bottom portion of the gap. According to FIG. 5, the wet etch resistance of SiO₂ film at the side-bottom portion of the gap may improve about 31% at 3 Torr compared to the wet etch resistance at 5 Torr.

FIG. 6 shows a WER of SiO₂ film deposited on the inner wall of the gap per position of the gap in accordance with the power of low radio frequency component under the common condition of 3 Torr of process pressure, 1200 W of high radio frequency component and one second of RF supply time. The high and low radio frequency components may be supplied for one second. In more detail, FIG. 6 shows WER when the power of the low radio frequency component is 0 W (no LRF), 100 W and 300 W respectively with 1200 W of high radio frequency component supplied for one second.

The case of 0 W of low radio frequency component where low radio frequency component is not supplied, is comparable to the process results carried out at 3 Torr in FIG. 5, the same pressure as FIG. 6, in which the wet etch rate of SiO₂ film at the side-bottom portion of the gap may be reduced from 7.9 to 6.5 when the high radio frequency component may be increased from 900 W (FIG. 5) to 1200 W (FIG. 6). In other words, a wet etch resistance may improve and a denser film may be deposited by increasing an ion bombardment effect when the high radio frequency component is solely supplied.

FIG. 6 shows that the more the low radio frequency component power is increased from 100 W to 300 W, the more the wet etch resistance at the bottom portion of the trench may improve accordingly. FIG. 6 also shows that the more a low radio frequency component power may be increased, the more the differences of wet etch resistance between side-top and side-middle and side-bottom may be reduced, and the wet etch resistance (or wet etch rate) between them becomes uniform. For instance, the wet etch rate of SiO₂ film at each portion is 3.4 at the side-top portion, 3.7 at the side-middle portion and 4.6 at the side-bottom portion when the low radio frequency component power may be increased from 0 W to 100 W to 300 W, reducing the difference of the wet etch rate.

FIG. 7 shows the trend of wet etch rate (or wet etch resistance) of SiO₂ film at the side-bottom portion of the trench according to process pressure, high radio frequency component power (HRF power) and low radio frequency component power (LRF power) where both radio frequency component powers are supplied for one second.

In FIG. 7, a wet etch resistance may be maximized and the film may be much denser when a low process pressure, high radio frequency component power and low radio frequency component power are applied at the same time. For instance, when the high radio frequency component power and the low radio frequency component power are supplied at 3 Torr at the same time, that is condition d, the wet etch resistance may be improved by about 55% compared to that at 5 Torr, that is condition a. Therefore, by combining a high radio frequency component, a low frequency component at low process pressure, a film with high and more uniform wet etch resistance may be deposited on the inner wall of the gap.

In FIG. 7, the wet etch resistance of the film at the low part of the side wall of the gap may be the lowest and densified the most in condition d in which the pressure is 3 Torr, and the high radio frequency component power and the low radio frequency component power are 1200 W and 300 W respectively, that is, 3:1 of radio frequency component power ratio. But the ratio of high radio frequency component power and low frequency component power is not limited thereto. The high radio frequency component power and the low radio frequency component power may be provided in the range of the ratio of 1:1 to 3:1.

According to the process results in FIG. 5 to FIG. 7 and Table 1 above, it may be desirable to maintain a process pressure at less than 3 Torr and increase the power of high and low radio frequency components within the range of not generating a parasitic plasma around the reactor and not discharging the radio frequency electromagnetic radiation to the outside of the reactor so that radicals may reach the bottom portion of the gap and contribute to forming a dense film. It may also be desirable to provide the high radio frequency component power and low radio frequency component power in the range of ratio of 1:1 to 3:1. Therefore a gap having a high aspect ratio of more than 20:1, especially, may be filled with a dense film uniformly.

In Table 1, FIG. 5 to FIG. 7, 13.56 MHz of high radio frequency component and 430 kHz (=0.43 MHz) of low radio frequency component may be provided, but it is not limited thereto. In another embodiment a high radio frequency component in the range of 12 MHz to 60 MHz and a low radio frequency component in the range of 0.3 MHz to 2 MHz may be provided.

In addition to FIG. 4, FIG. 8 illustrates other embodiments. In the radio frequency electromagnetic radiation supply step in FIG. 8A, a high radio component is supplied first, followed by supplying a low radio frequency component subsequently. This enables radicals to move to the gap after being generated in a reaction space, giving enough time for radicals to reach the bottom of the gap. In FIG. 8A high and low radio frequency components are supplied sequentially, but in another embodiment, they may be overlapped. That is, a low radio frequency component supply may start before a high radio frequency component supply ends.

In another embodiment of FIG. 8B, a high radio frequency component and a low radio frequency component are supplied in pulses and the duty ratio, i.e. the ratio of plasma on/off time, may be set so that the plasma damage to the substrate caused by radicals and active ions may be reduced. So, the embodiments of FIG. 8 may have another technical advantage in addition to the technical advantages according to FIG. 4. In another embodiment, at least one of high radio frequency component and low radio frequency component may be supplied in pulses.

The duty ratio may be defined as the ratio of the actual radio frequency electromagnetic radiation supply time to the unit cycle time of radio frequency electromagnetic radiation pulsing when the radio frequency electromagnetic radiation is provided in pulses.

FIG. 9 shows the definition of the duty ratio of a radio frequency electromagnetic radiation supply step in a PEALD process. When the radio frequency electromagnetic radiation is provided in a pulse, the ratio of the actual radio frequency electromagnetic radiation supply time b to the unit cycle time a of radio frequency electromagnetic radiation pulsing, that is b/a is defined as a duty ratio. In another embodiment according to this invention, the radio frequency electromagnetic radiation may be provided in a pulse in the range of duty ratio of 10% to 75%.

In another embodiment, the ratio of the high radio frequency component and the low radio frequency component may be adjusted to form a uniform film in density throughout the gap. FIG. 10 schematically illustrates a reactor structure for using the method. In FIG. 10 a gas supply unit 3 and a substrate supporting unit 4 are spaced apart and face each other, and the space between them forms a reaction space 13. The gas supply unit 3 may be metallic and may be a showerhead. A RF rod 14 is disposed on one side of the gas supplying unit 3. The RF rod 14 is disposed between a radio frequency electromagnetic radiation generation unit 9 and a gas supplying unit 3, and delivers radio frequency electromagnetic radiation generated in the radio frequency electromagnetic radiation generation unit 9 to the gas supplying unit 3. The substrate supporting unit 4 may be a heating block which may include a substrate loading unit (not shown) on it. The substrate supporting unit may be a susceptor. A gas inlet 5 may be connected to one side of reactor wall 2 surrounding a reactor 1 through a reactor wall 2. A gas may be provided to the substrate 6 through the gas inlet 5, a gas supplying unit 3 and a reaction space 13. Reaction byproducts may be exhausted through an exhaust path 7 connected to another side of the reactor 2 and an exhaust unit 8 which may include an exhaust pump.

In FIG. 10 radio frequency electromagnetic radiation generation unit 9 may include a high radio frequency component power generator 10, a low radio frequency component power generator 11 and a matching network 12. The radio frequency component power generated in the radio frequency component power generators 10, 11 may be delivered to the gas supplying unit 3 through a matching network and a RF rod 14. In FIG. 10 a gas supplying unit 3 is an upper electrode and a substrate supporting unit 4 facing the gas supplying unit 3 is a lower electrode and the plasma is generated in the reaction space 13 by activating gas provided thereto.

Without increasing radio frequency electromagnetic radiation supply time and its power too much, a film with uniform wet etch resistance may be formed on the inner wall of the trench having high aspect ratio by combining a high radio frequency component and a low radio frequency component at low process pressure. So seams, voids or cracks may be prevented from occurring in the film filling a gap in the subsequent heat treatment step. 

What is claimed is:
 1. A substrate processing method comprising: providing a substrate with a trench in a reaction chamber; pumping down the reaction chamber to a pressure at or below 5 Torr; and, filling the trench with a film by a deposition cycle comprising: supplying a precursor; supplying a reactant; and, supplying a radio frequency electromagnetic radiation comprising a relatively high radio frequency component and a relatively low radio frequency component.
 2. The method according to claim 1, wherein the method comprises providing the relatively high radio frequency component and the relatively low radio frequency component at the same time.
 3. The method according to claim 1, wherein the method comprises providing the relatively high radio frequency component and the relatively low radio frequency component sequentially.
 4. The method according to claim 3, wherein the relatively high radio frequency component and the relatively low radio frequency component are partially overlapping.
 5. The method according to claim 2, wherein, at least one of the high radio frequency component and the low radio frequency component are supplied in pulses of duty ratio of approximately 10% to 75%
 6. The method according to claim 1, wherein the reaction chamber is pumped down to a pressure less than 4 Torr or even 3 Torr or less.
 7. The method according to claim 1, wherein the precursor is at least one of aminosilane, iodosilane and silicon halide or a combination thereof.
 8. The method according to claim 7, wherein the precursor is at least one of DIPAS, SiH₃N(iPr)₂, TSA, (SiH₃)₃N, DSO, (SiH₃)₂, DSMA, (SiH₃)₂NMe, DSEA, (SiH₃)₂Net, DSIPA, (SiH₃)₂N(iPr), DSTBA, (SiH₃)₂N(tBu), DEAS, SiH₃NEt₂, DTBAS, SiH₃N(tBu)₂, BDEAS, SiH₂(NEt₂)₂, BDMAS, SiH₂(NMe₂)₂, BTBAS, SiH₂(NHtBu)₂, BITS, SiH₂(NHSiMe₃)₂, TEOS, Si(OEt)₄, SiCl₄, HCD, Si₂Cl₆, 3DMAS, SiH(N(Me)₂)₃; BEMAS, SiH₂[N(Et)(Me)]₂; AHEAD, Sit (NHEt)₆; TEAS, Si(NHEt)₄; Si₃H₈; DCS, SiH₂Cl₂; SiHI₃, SiH₂I₂ or a combination thereof.
 9. The method according to claim 1, wherein the reactant is at least one of O₂, O₃, N₂O and CO₂ or a combination thereof.
 10. The method according to claim 1, wherein the method comprises purging in between supplying a precursor or a reactant and supplying radio frequency electromagnetic radiation.
 11. The method according to claim 1, wherein the method comprises providing a reactant continuously throughout the cycle.
 12. The method according to claim 6, wherein a wet etch rate and a density of the film filling a gap is uniform throughout the trench.
 13. The method according to claim 1, wherein at least one of the high radio frequency component and the low radio frequency component are supplied in-situ.
 14. The method according to claim 1, wherein the power ratio of the high radio frequency component and the low radio frequency component is approximately 1 to 1 to 3 to 1 to form a uniform film in density throughout the trench.
 15. The method according to claim 1, wherein the frequency of the high radio frequency component is approximately 12 to 60 MHz and the frequency of the low radio frequency component is approximately 0.3 to 2 MHz. 